1. Field of the Invention
Embodiments of the present invention relate to ultrasound imaging probes, and particularly, to flexible, single chip, CMUT based ultrasound imaging probes using various monolithically integrated CMUT arrays on CMOS electronics.
2. Background of Related Art
Side-looking intravascular ultrasound (“IVUS”) imaging probes exist that provide relatively high resolution images of tissue and fluid. This can be useful, for example, when inspecting the inside surfaces of vessels or tissues immediately surrounding the vessel. Similarly, intracardiac echocardiography (“ICE”) probes also exist which use one-dimensional (1-D) imaging arrays.
Unfortunately, current commercial IVUS imaging systems offer only side-looking capabilities and cannot generate images of, for example, the volume in front of the catheter. ICE probes, for example, provide only two-dimensional cross sections, but not volumetric images. The ability to image fluid and/or tissue directly in front of the probe can be useful in a number of applications. An IVUS catheter that can provide forward-looking (FL) volumetric ultrasound images would be a valuable clinical tool for, for example and not limitation, guiding interventions in coronary arteries, for the treatment of chronic total, or near-total, vascular occlusions, and for stent deployment. See, e.g., FIGS. 1a-1b. 
In order to navigate tortuous arteries and coronary structures, for example, an important aspect of IVUS and ICE probes is the size and flexibility of the probes. As a result, the rigid section of the probe close to the imaging tip should be as short and as small in diameter as possible. Current ultrasound array probes used for these purposes are rigid over several millimeters, limiting their maneuverability.
Similarly, for improved flexibility, among other things, the number of electrical connections connecting the probe to the back end imaging system should also be limited. In other words, a larger number of cables make the catheter less flexible. The number of external connections is also important, for example, because excessive external connections increase probe size, manufacturing cost, and complexity.
In addition, to enable the probe to enter small areas (e.g., blood vessels), for example, the frontal area of the probe must be limited. To obtain the better resolution given the limited area of the probe, however, the transmit (Tx) and receive (Rx) array elements can be placed in sparse arrays around substantially the entire chip surface and can comprise integrated electronics for control. Furthermore, where possible, the Tx and Rx array elements should be separated and may further comprise dummy elements to achieve high signal to noise ratio with minimal cross-talk. In addition, phasing and other control features can enable ultrasound beam forming to enable the shape and/or direction of the ultrasound radiation to be altered for imaging purposes.
What is needed, therefore, is a single chip, flexible, forward-looking ultrasonic probe. The probe should comprise various optimized chip layouts. The probe should comprise improved resolution, reduced imaging time, reduced cross-talk, and improved beam direction and shaping. It is to such an ultrasonic probe that embodiments of the present invention are primarily directed.